A torque converter of an automatic transmission is provided with a lockup clutch capable of directly coupling an input side and an output side, and an engagement capacity of the lockup clutch is controlled hydraulically in accordance with an operating condition of a vehicle.
A relationship between a command oil pressure for the lockup clutch and an actual engagement capacity of the lockup clutch varies with individual differences and the passage of time, and therefore the command oil pressure employed during engagement of the lockup clutch is conventionally subjected to learning control. For example, in JP05-141528A, an excess or deficiency in the command oil pressure is learned on the basis of a decrease width of an engine rotation speed at a point where the lockup clutch acquires engagement capacity, and the next command oil pressure for the lockup clutch is corrected on the basis of this excess or deficiency.